190 MORPHOLOGY AND EVOLUTION
aspect of the first raetacarpal in the Gibbon. The adductor obliquus pollicis arises from carpal bones in Man and all the Apes except the Orang. It is inserted along with the transverse muscle. Halford (83) applied the name " contrahentes " to a small group of muscles which adduct the thumb and fingers. In the Gorilla the adductores transversus and obliquus are the only contrahentes ; in the Orang additional fibres run from the septum on the third metacarpal to the palmar interossei; in the Chimpanzee there are two adductores pollicis, and adductors of the annularis and minimus all having a common origin : in the Gibbon the contrahentes adduct all digits except the medius.
The extensor carpi radiales longior and brevior, extensor carpi ulnaris and supinator brevis are as in Man.
The supinator longus: arises from the external humeral condyle, and from the external intermuscular septum; it may reach the deltoid insertion in the Chimpanzee. It is inserted into the lower part of the shaft of the radius.
The extensor communis digitorum arises from the external condyle of the humerus, the fascia over it, and the septa on each side. It sends tendons to the bases of the ungual phalanges of the fingers as in Man, and there are expansions over the interphalangeal joints.
The extensor TninlTni digiti arises in the Chimpanzee and Orang from the external condyle and the fascia over the anconeus; in the Gibbon and Gorilla it also rises from the septum between the extensor communis and extensor carpi ulnaris. It is inserted into the base of the ungual phalanx of the minimus in all the Apes except the Orang, in which it is inserted with the